The effect of mono- and multiple fermentation parameters on volatile fatty acids (VFAs) production from chicken manure via anaerobic digestion

[Display omitted] •Optimal conditions for VFAs production from CM via AD was evaluated at 37 °C.•Highest net VFAs yield of 0.53 g-VFA/g-VS was achieved with heat shocking.•Acetate, propionate and butyrate were the dominant VFAs with ratio of 7:1.5:1.5.•Through a 16-day digestion period, maximum amount of VFAs can be achieved.•Alkaline pH was suggested as an effective promoter for VFAs production from CM. Although the high nitrogen content of chicken manure (CM) poses major challenges for methane production through anaerobic digestion, on the bright side, it has a great potential for production of value-added intermediate products, such as volatile fatty acids (VFAs). However, in order to enhance VFAs yield, methane formation should be substantially suppressed. In the current research, individual and multiple effects of initial pH, heat-shock pretreatment, chemical methanogens inhibitor and the inoculum to substrate ratio (ISR) on optimization VFAs fermentation from CM were evaluated via batch assays. In this regard, the highest net VFAs yield, 0.53 g-VFA/g-VS, was achieved at conditions with heat-shocked inoculum and CM at ISR 1:6 and pH uncontrolled. Acetate dominated the VFAs mixture, accounting for up to 75% of total. Increased inoculum content enhanced the bioconversion efficiency to 78% at ISR 1:3. The study results suggest that alkalinity is a key promoter of VFAs production from CM.